Prosthetic ankle and foot combination

ABSTRACT

A prosthetic ankle and foot combination has an ankle joint mechanism constructed to allow damped rotational movement of a foot component relative to a shin component. The mechanism provides a continuous hydraulically damped range of ankle motion during walking with dynamically variable damping resistances, and with independent variation of damping resistances in the plantar-flexion and dorsi-flexion directions. The mechanism also provides for adjustment of a second piston element with respect to a shin component when a first valve is closed and a locking valve is open to adjust a reference angular position independently of the damping function that occurs during walking. An electronic control system coupled to the ankle joint mechanism includes at least one sensor for generating signals indicative of a kinetic or kinematic parameter of locomotion, the mechanism and the control system being arranged such that the damping resistances effective over the range of motion of the ankle are adapted automatically in response to such signals. Single and dual piston hydraulic damping arrangements are disclosed, including arrangements allowing independent heel-height adjustment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 12/035,717 filedFeb. 22, 2008, which is now U.S. Pat. No. 7,985,265, and which claimsthe benefit of Provisional Application No. 60/891,075 filed Feb. 22,2007. U.S. application Ser. No. 12/035,717 is a continuation-in-part ofU.S. application Ser. No. 11/956,391 filed Dec. 14, 2007, which is nowU.S. Pat. No. 8,574,312, and which claims the benefit of ProvisionalApplication No. 60/869,959 filed Dec. 14, 2006. The entire contents ofsuch applications are incorporated by reference in the presentapplication.

FIELD OF THE INVENTION

This invention relates to a prosthetic ankle and foot combinationarranged to allow damped ankle flexion. The invention also includes alower limb prosthesis incorporating such an ankle and foot combination.

BACKGROUND OF THE INVENTION

Current prosthetic ankle-foot systems are generally aligned foroperation as fixed mechanical structures comprising elastic anddeformable elements designed to provide stability during standing andwalking and to return energy for propulsion into the swing phase of thewalking cycle. However, such a device is often uncomfortable for theuser whilst standing and walking on ramps and stairs and walking atdifferent speeds. Users have also experienced knee instability anddifficulty in maintaining forward motion during roll-over of the footwhile standing and walking on ramps and stairs, with consequentimpairment of efficiency. These difficulties are particularly importantfor transfemoral amputees whose stance phase action is normallycompromised by significantly reduced knee flexion and extension whichwould otherwise assist shock absorption and forwards propulsion duringthe stance phase.

Another aspect of ankle-foot function and transfemoral amputeelocomotion relates to the way in which a typical known prosthesishinders the amputee, resulting in poor body posture for certainlocomotion activities such as ascending and descending stairs and ramps,which diminishes the potential for application of voluntary control,particularly user-generated hip extension torque. The poor posturedescribed is largely caused by inappropriate stiffness and range ofmotion at the ankle which does not allow the body centre of mass to passeasily over the ankle. Consequently, amputees sometimes have to adoptunnatural compensating actions.

An ankle joint mechanism allowing dynamic hydraulic control of theangular position of a prosthetic foot with respect to a shin componentis disclosed in Mauch Laboratories, Inc., Hydraulik Ankle Unit Manual,March 1988. The shin component is attached to a vane piston housed in afluid-filled chamber with a concave part-circular lower wall. Agravity-controlled ball rolls forwards and backwards on the wallaccording to the orientation of the foot to open or close a bypasspassage in the piston. As a result, dorsi-flexion of the mechanism isprevented when the shin component is vertical, largely irrespective ofwhether the foot is horizontal or inclined downwardly or upwardly. Sucha prosthesis also suffers partly from the disadvantages described above.

In US2002/0138153 (Koniuk) a self-adjusting ankle with a similarfunction is disclosed. This unit switches between two damping resistancelevels, the switch between the two damping levels being triggered bydetection of a shin pylori reaching a vertical orientation. The seconddamping level is set effectively to prevent pivoting of the foot.

Amongst other known prosthetic ankle systems is that of U.S. Pat. No.3,871,032 (Karas). This system contains a damping device having a dualpiston and cylinder assembly with tappet return springs actingcontinuously to return the ankle to a neutral position. EP-A-0948947(O'Byrne) discloses a prosthetic ankle having a ball-and-socket jointwith a chamber filled with a silicone-based hydraulic substance, thejoint having a visco-elastic response. In one embodiment, the chambercontains solid silicone rubber particles suspended in a silicone fluidmatrix. US2004/0236435 (Chen) discloses a hydraulic ankle arrangementwith adjustable hydraulic damping and resilient biasing members mountedanteriorly and posteriorly of an ankle joint rotation axis. InWO00/76429 (Gramtec), a leg prosthesis is described having an anklejoint allowing heel height adjustment by way of a hydraulic piston andlinkage arrangement. Elastic components absorb shock during walking.US2006/0235544 (Iversen et al) discloses a hydraulic ankle mechanismwith a rotary vane.

The electronically controlled ankle disclosed in WO2003/086245 (Martin)has a magnetorheological (MR) fluid-controlled ankle component.WO2007/027808 (Ossur) discloses an electronically controlled ankle jointin which the angle of foot springs about an ankle joint is altered bymeans of a motorised coupling.

It is an object of the present invention to provide a more naturalfunction in a variety of situations.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, a prosthetic ankleand foot combination comprises a foot component and an ankle jointmechanism, the ankle joint mechanism including a shin component andbeing constructed to allow damped rotational movement of the footcomponent relative to the shin component about a medial-lateral jointflexion axis, wherein: the ankle joint mechanism is arranged to providea continuous hydraulically damped range of ankle motion during walkingwith dynamically variable damping resistances associated with anklemotion in the plantar-flexion and dorsi-flexion directions respectively;the combination further comprises a control system coupled to the anklejoint mechanism having at least one sensor for generating signalsindicative of a kinetic and/or kinematic parameter of locomotion and/orwalking environment; and the ankle joint mechanism and the controlsystem are arranged such that the damping resistances effective over thesaid range of motion and associated with motion in the plantar-flexionand dorsi-flexion directions are adapted automatically in response tothe said signals. Preferably, the damping resistance is the predominantresistance to ankle joint flexion over at least part of the said rangeof ankle motion.

Advantageously, the control system is programmed to generate signalindicative of terrain, e.g. ground inclination, and to vary the degreeof damping resistance in the direction of both ankle dorsi-flexion andankle plantar-flexion. Particular benefits are achieved if the dampingresistance in the direction of plantar-flexion is automaticallydecreased when the control system generates signals indicative ofwalking down an incline and increased when indicative of walking up anincline, compared with a level of resistance in that direction set forwalking on the level. Conversely, it is preferable that the controlsystem operates such that the damping resistance in the direction ofdorsi-flexion is increased compared with the level walking resistancelevel in the dorsi-flexion direction when the control system signals areindicative of walking down an incline and decreased when the signals areindicative of walking up an incline.

The control system may also be capable of detecting walking on stairs asanother kind of terrain variation. In such a case, the dampingresistance may also be automatically adjusted in response to signalsgenerated by the control system, the resistance in the direction ofplantar-flexion being decreased when the signals are indicative ofwalking upstairs and increased when the signals are indicative ofwalking downstairs.

Another parameter that may be used for altering damping resistance iswalking speed (or step period or its reciprocal step rate, commonlyreferred to as “cadence”). As the speed of walking or cadence valueincreases, the control system preferably decreases the resistance of thehydraulic damping in the direction of dorsi-flexion. Conversely, whenthe user is walking more slowly, the resistance in the direction ofdorsi-flexion is increased. In addition, resistance in theplantar-flexion direction is increased when walking faster and decreasedwhen walking slower.

Various ways of indicating kinetic or kinematic parameters of locomotionmay be used. One preferred sensor is an accelerometer, typically atwo-axis accelerometer, mounted in the foot component. It will beappreciated that such an accelerometer can produce signals indicative offoot component inclination, as well as gait characteristics such asacceleration or deceleration at heel strike. Foot component angularvelocity can also be measured by processing the sensor output in thecontrol system to integrate the acceleration output over time.Techniques for processing output signals from an accelerometer to obtainkinetic and kinematic parameter data such as those referred to above areset out in Morris, J. W “Accelerometry—A Technique for the Measurementof Human Body Movements”, Journal of Biomechanics, 1973, pages 726-736.Additional information is contained in Hayes, W. C et al. “Leg MotionAnalysis During Gait by Multiaxial Accelerometry: TheoreticalFoundations and Preliminary Validations”, Journal of BiomechanicalEngineering, 1983, vol. 105, pages 283-289. The content of these papersis incorporated in this specification by reference.

A second sensor is also, preferably, provided in the form of, forinstance, a magnetic transducer sensing the relative position of thefoot component and the shin component. This may be performed by directmeasurement of the relative angular position or by sensing the lineardisplacement of one element of the ankle joint mechanism with respect toanother in the case of the mechanism including, for instance, a linkageconverting relative rotational movement of the foot component withrespect of the shin component to relative translational movements.

Such a sensor may be used for sensing cadence (step rate) and theamplitude of ankle flexion. Measurement of the piston stroke indicatesthe magnitude of flexion. Changes to the signal characteristics may beused to indicate indirectly step rate, for example, the time taken toreach a particular flexion angle or, alternatively, measurement of thetime taken for the ankle angular velocity to indicate a change fromplantar-flexion to dorsi-flexion.

Hydraulic damping resistance is preferably introduced in the prosthesisdescribed above by means of a joint mechanism in the form of a hydraulicpiston and cylinder assembly. In the case of this being a linear pistonand cylinder assembly, it is connected to an associated linkage arrangedto convert between translational piston movement and rotational relativemovement of the foot component and the shin component. The piston andcylinder assembly includes at least one damping control valve which isadjustable during locomotion by an actuator coupled to the valve. Thevalve is arranged such that, when adjusted, it varies the degree ofhydraulic damping resistance to the piston movement. Independent controlof damping resistance in the directions of dorsi-flexion andplantar-flexion may be achieved by having two such valves withrespective associated non-return valves.

In preferred embodiments of the invention, control of the dampingresistance is such that, at an angular position within at least part ofthe range of ankle motion, the resistance can be any of several (e.g. atleast three) different levels. Indeed, the resistance is preferablycontinuously variable. It is possible to maintain the dampingresistance, preferably in the case of both resistance to plantar-flexionand resistance to dorsi-flexion, at a set level so long as the walkingcharacteristics indicated by the sensor or sensors of the control systemdo not change. This means, for instance, that a valve in a hydrauliccircuit within the ankle joint mechanism can be adjusted to any ofseveral different positions having respective different orifice areasaccording to signals produced by the control system and that, once thevalve has been adjusted to provide a particular orifice area, no furtheradjustment of the valve may be needed so long as the walkingcharacteristics or parameters indicated by the sensors do not change.This has advantages in terms of minimising power consumption. However,when power and energy limitations permit it, the damping resistance canbe altered on each step such that, for example, the resistance to motionin the direction of dorsi-flexion can be increased as the angle ofdorsi-flexion increases, i.e. increasing from a variable resistancelevel governed by signals generated in the control system in response tosensor outputs, to a higher level of resistance beyond a givendorsi-flexion angle. Different damping resistance relationships tosensed walking characteristics may be used, as follows.

The change in damping resistance may be linearly proportional to asensed characteristic such as ground inclination or walking speed. Thismay apply to one or both of resistance in the direction of dorsi-flexionand resistance in the direction of plantar-flexion.

The change in damping resistance may follow a predetermined non-linearfunction (e.g. according to a square law or other polynomial) withrespect to the sensed characteristic.

Changes in ground inclination may be sensed indirectly by measuring agait characteristic such as the timing or duration or specific gaitevents or phases, e.g. the time taken for the foot to reach a flat-footstate or to stop plantar flexing after heel-strike. In such a case, theresistance to movement in the direction of plantar-flexion may beadjusted to prevent the duration of plantar-flexion exceeding apredetermined maximum. In particular, the maximum plantar-flexionduration allowed is never greater or less than a predefined orprogrammable time, depending on walking requirements.

The change in damping resistance may also be governed as a function of agait measurement such as the acceleration recorded at heel-strike. Insuch a case, the resistance in the direction of plantar-flexion isadjusted to limit the maximum acceleration occurring during the loadingresponse phase of gait to a predetermined or programmed value.

Changes in damping resistance may be determined from a function which isa combination of measured gait characteristics such as walking speed,cadence, surface inclination, stride-length and changes in step height(e.g. up or down a step) or any another kinetic or kinematic parametermeasured during locomotion.

The changes in resistance in the direction of plantar-flexion anddorsi-flexion respectively may be mutually adapted, i.e. according toone another. Thus, in the case of walking down an incline, a decrease inplantar-flexion resistance compared with the value for level walking,may be automatically accompanied by an increase in dorsi-flexionresistance by a predetermined or programmable factor.

Changes in damping resistance may be specifically programmed underdifferent trial conditions with specific parameter values, such dampingresistances being stored in a memory in the control system, the systembeing programmed such that during normal use (i.e. during a playbackphase as opposed to a teaching phase) appropriate damping resistancevalues are computed by interpolation between stored values when thesensed parameters lie between the parameter values used for programming.

According to another preferred scheme of operation, the control systemmay store a database of damping resistance settings for movement in bothdorsi-flexion and plantar-flexion directions, which database is derivedfrom clinical testing data. In this embodiment, a look-up table ofsettings is stored in the control system memory. The stored data isobtained from test results with a variety of users, rather than valuesobtained specifically for the individual user.

Depending on the provision of heel-adjustment means in the mechanism,changes in damping resistance may be derived from a calibration routinewhereby the damping resistance variation is optimised according todifferent heel heights, the calibration being performed in the same wayas surface gradient calibration.

The sensitivity of changing damping resistance in response to changingwalking requirements may be defined in different ways. For instance, thechanges in walking requirements may be determined on an individualstep-by-step basis. Alternatively, the changes in walking requirementmay be determined based on a measured average of a previous number ofsteps of a specific variable such as gait speed and inclination or othermeasured gait variable. The changes in walking requirements may besubdivided into bands defining response sensitivity. For instance,walking speed may be subdivided into cadence (step-rate) bands orranges. Similarly, changes to ground inclination may be subdivided intobands of a few degrees at a time. The limits of such bands may beuniformly distributed over the range of the relevant parameter orcharacteristic, or non-uniformly. Such limits may be predetermined orprogrammable, or they may be continuously or step-wise self-adaptive,such adaptation being based on clinical testing with a variety ofamputees or upon responses measured with an individual user. Anotheraspect of the invention provides a lower limb prosthesis comprising ashin component, a foot component, and a joint mechanism interconnectingthe foot and shin components and arranged to allow damped pivoting ofthe foot component relative to the shin component about a medial-lateraljoint flexion axis during use, wherein the joint mechanism comprises ahydraulic piston and cylinder assembly and an associated linkagearranged to convert between translational piston movement and rotationalrelative movement of the foot component and the shin component, thepiston and cylinder assembly including an adjustable damping controlvalve arranged to vary the degree of hydraulic damping resistance to thesaid translational piston movement at least insofar as such movement isassociated with flexion of the foot component relative to the shincomponent, and wherein the prosthesis further comprises a valve controlsystem including at least one sensor for generating signals indicativeof a kinetic or kinematic parameter of locomotion and, coupled to thecontrol valve, an actuator for adjusting the valve, the control systembeing arranged to adjust the valve during locomotion thereby to vary thehydraulic damping resistance of the joint mechanism to flexion inresponse to the signals from the sensor. The invention also includes aprosthetic ankle and foot combination and a prosthetic ankle joint eachhaving the above features.

As described above, the way in which damping resistance may be variedcan be programmable so that, for instance, the control system isarranged to have a “teach” mode in which a prosthetist may select andstore damping resistance settings for different speeds of walking anddifferent terrains (e.g. ascending stairs or an incline, descendingstairs or an incline, and walking on level ground), these settings beingdetermined during test sessions with the amputee. Alternatively, aself-tuning system may be used whereby control parameters areautomatically adjusted towards specific values under known walkingconditions. As a further alternative, settings may be stored in adatabase or as a look-up table derived from clinical tests on a varietyof patients, the settings having related to sensed or computedparameters. A combination of these methods may be used.

In accordance with the principle outlined above, the valve controlsystem may be arranged to generate a signal indicative of a kinetic orkinematic parameter which varies during individual gait cycles and todrive the valve so as to increase and decrease hydraulic resistance toflexion during each of a plurality of gait cycles, the direction,magnitude and timing of such changes in resistance being dynamicallyadjustable during locomotion. In one embodiment the system operates suchthat the hydraulic resistance to dorsi-flexion is increased to a maximumvalue during the stance phase of the gait cycle, the time at which themaximum value is reached being altered in the stance phase, for exampleoccurring later in the stance phase, when the signal indicative ofterrain indicates walking down stairs or up an incline compared with thetime at which the maximum value is reached when the said signalindicates walking on level ground.

According to another aspect of the invention, a prosthetic ankle andfoot combination comprises a foot component and a hydraulic ankle jointmechanism, the ankle joint mechanism including a proximal shin componentand being constructed to allow damped rotational movement of the footcomponent relative to the shin component about a medial-lateral jointflexion axis, wherein the ankle joint mechanism is arranged to provide(a) continuous hydraulically damped ankle flexion during walkingrelative to a present reference angular position of the foot componentwith respect to the shin component and (b) adjustment of the referenceangular position. The adjustment of the reference angular position mayalso be damped, preferably hydraulically, and may be user adjustable.Once the reference angular position has been set, the range ofrotational movement of the foot component relative to the shin componentis preferably a single fixed range. Within that range or at least amajor part of it, adaptive damping control is effected, the relationshipbetween damping resistance levels being defined according to changingrequirements of locomotion such as terrain (surface inclination and/orstairs, and walking speed or cadence). Within the range of rotationalmovement, damping resistance is preferably continuously variable orvariable in a series of steps such that, typically, whilst the walkingrequirements remain constant, a programmed damping resistance level in agiven direction (plantar-flexion, dorsi-flexion, or both) is maintainedthroughout the gait cycle and remains constant from step-to-step. It isalso possible for dynamic damping of flexion during walking to bemanually varied rather than automatically adaptively varied.

In such a combination, the mechanism preferably comprises a piston andcylinder assembly having a first piston element movable in a cylinder todrive hydraulic fluid through an orifice in response to rotation of thefoot component relative to the shin component, the mechanism furthercomprising a first valve defining the orifice and an electrical actuatorfor driving the valve to vary the area of the orifice thereby to providedynamically variable hydraulic damping of ankle flexion during walking.

The mechanism may comprise a second valve element defining anotherorifice through which hydraulic fluid is driven when the first pistonelement moves in response to rotation of the foot component relative tothe shin component, the first and second valves being constructed andarranged such that the first valve and the second valve independentlydetermine the damping resistance of the mechanism to flexion in thedorsi-flexion and plantar-flexion directions respectively.

The damped adjustment of the reference angular position may be performedby arranging for the mechanism to comprise further a second pistonelement and a locking valve, wherein the second piston element isarranged to drive hydraulic fluid through the locking valve in responseto rotation of the foot component relative to the shin component, andthe locking valve can be closed to lock the second piston elementthereby to set the reference angular position of the foot component withrespect to the shin component.

Accordingly, in one preferred embodiment, the ankle joint mechanismcomprises a hydraulic piston and cylinder assembly and an associatedlinkage arranged to convert between translational piston movement androtational relative movement of the shin component and the footcomponent; the piston and cylinder assembly comprises first and secondpiston elements which are substantially coaxial and substantiallyaligned with the shin axis; the first piston element has a neutralposition in the assembly and is located in a cylinder so as to drivehydraulic fluid through an orifice when moved from the neutral positionin response to pivoting of the foot component from a preset referenceangular position relative to the shin component, the fluid flow throughthe orifice damping the said pivoting; and the second piston element isarranged to drive hydraulic fluid through a locking valve in response topivoting of the foot component relative to the shin component, whichvalve can be closed to lock the second piston element thereby to set thesaid reference angular position corresponding to the neutral position ofthe first piston element. In this way it is possible to allowdorsi-plantar-flexion of the ankle over a limited range of movement withlargely damped, as opposed to resilient, resistance to motion, resultingin an ankle which is able easily to flex under load according tochanging activity requirements without generation of high reactionmoments which would otherwise cause discomfort and compromise thefunction of the prosthesis.

The position of the foot component relative to the shin component at agiven position of the first piston element may be independently adjustedby opening the normally closed locking valve and causing the secondpiston element to move in the assembly until a required relativeorientation of the foot component and the shin component is reached,whereupon the locking valve is closed again. The “given position” of thefirst piston element is referred to above as the neutral position.Although this so-called neutral position may be defined by resilientelements in the mechanism biasing the first piston element towards aparticular position in the cylinder, the “neutral” position may benotional in the sense that it is not defined by any characteristic orfeature of the piston and cylinder assembly as such, but may be merely aposition selected by the user or prosthetist for the purpose of settingthe reference angular position by adjusting the position of the secondpiston element.

Preferably an interlocking device is provided to lock the first pistonelement whilst this adjustment is being made. This adjustment allowscontrol of dorsi- and/or plantar-flexion of the ankle to be performedwith reference to a selected reference angular position of the footcomponent and the shin component, this reference orientation of onecomponent relative to the other being selected according to, e.g., shoeheel-height or to achieve particular functional characteristics requiredby the user's prosthetist. It will be noted that the ability to set thereference angular position independently of the damping function, andwithout moving the first piston element, has the effect of maintainingthe effective range of dorsi- and/or plantar-flexion of the ankle duringuse of the prosthesis irrespective of shoe heel-height.

The piston and cylinder assembly can be constructed in a number ofdifferent ways. In one embodiment of the invention, one of the pistonelements is slidable in a bore formed in the other piston element. Oneof the piston elements may form a transversely extending movable wall ofa chamber which houses the other piston element.

In the case of one piston element being slidable in a bore formed in theother, the former element may comprise two pistons interconnected by apiston rod which slides in the bore as well as being slidable within thecylinder referred to above. The space between the two pistons contains adividing wall dividing the space into two variable volume chambersinterconnected by a first passage containing a valve element. This valveelement is typically drivable over a range of positions by a servo motoror a stepper motor under electronic control in order to vary the area ofthe orifice and, therefore, the resistance to movement of the firstpiston element and, consequently, rotation of the ankle joint during use(i.e. during locomotion, whether it be walking, running, climbing ordescending ramps and stairs, and so on). Such an arrangement may beduplicated, albeit with oppositely directed respective non-return valvesas well, for servo or stepper motor controlled damping resistancesindependently for the directions of dorsi-flexion and plantar-flexion,as will be described in more detail below.

In this preferred embodiment, the so-called “other” piston elementconstitutes at least part of the dividing wall, both piston elementsbeing slidable within a common cylinder. Conveniently, both pistonelements are dual piston components, each having two pistonsinterconnected by a respective piston rod, the cylinder being atransverse wall dividing the space between the two pistons of the pistonelement having the above-mentioned internal bore. This transverse wallcontains a valved second passage linking the chambers formed on oppositesides of the transverse wall. It is preferably this second passage withwhich the locking valve is associated, the first passage or passagescontaining the damping orifice.

Alternatively, as in another embodiment of the invention, the piston andcylinder assembly comprises two cylinder units which are pivotallyinterconnected and which house the first and second piston elementsrespectively. The piston element in one of the cylinder units ispivotally connected to the other cylinder unit such that its movement isassociated with pivoting of one cylinder unit with respect to the other.This other cylinder unit, and the piston element housed in it, arepivotally connected to either the foot component or the shin componentsuch that movement of the respective piston element is associated withpivoting of the other cylinder unit with respect to the foot or shincomponent to which is it pivotally connected. Where the above-mentionedother cylinder unit is pivotally connected to the foot component, thefirst mentioned cylinder unit forms part of the shin component, and viceversa. In effect, the piston and cylinder assembly comprises twocylinder units stacked one above the other, operation of one beingassociated with relative pivoting of the shin component and anintermediate component and operation of the other being associated withrelative pivoting of the intermediate component and the foot component.Preferably, the cylinder unit which is located proximally, i.e. formingpart of or attached to the shin component, contains the locking valveand is, therefore, used for setting the reference angular position,whilst the other cylinder unit, located so as to be connected to thefoot component, serves to perform ankle joint damping. It is, however,possible to reverse the positions of the cylinder units. In any of theabove embodiments, the piston and cylinder assembly may include a valveelement operable to prevent fluid flow through the damping orifice. Theabove-mentioned interlocking device operates to prevent simultaneousopening of the valve element and the locking valve.

Advantageously, the interlocking device forms part of an electronicvalve control system including electrical actuators for the lockingvalve and the above-mentioned valve element, the control system beingconfigured to constrain operation of the actuators such that, at leastin normal circumstances, either the locking valve or the dynamicallyadjustable valve element is in its closed condition at any given time.The valve element may, itself, be part of a damping control valvedefining the damping orifice, the valve control system including atransducer or sensor adapted to produce an electrical signal indicativeof walking speed or terrain, the control system having a first outputcoupled to the damping control valve actuator and being arranged toproduce at such output an actuator drive signal which causes the dampingcontrol valve to vary the orifice area according to the indicatedparameter or parameters.

The preferred valve control system has a second output coupled to anelectrical actuator for the locking valve, which may be a servo motor ora solenoid, so that the valve control system can be used to open orclose the locking valve depending on whether a dynamic response mode ora setting mode is selected. In the dynamic response mode, actuator drivesignals are produced at the first and second outputs to cause thedamping control valve to be open to a degree depending on terrain andwalking speed, and the locking valve to be closed. Conversely, in thesetting mode, the actuator drive signals cause the damping control valveto close and the locking valve to open to allow setting of the saidreference angular position of the foot component relative to the shincomponent.

In other variants of the invention, differential control of theresistance to flexion in the dorsi direction and plantar directionrespectively may be provided using, for instance, two damping controlvalves in respective passages which function in parallel, i.e. oneallowing the flow of fluid in one direction from a variable volumechamber which varies in size with movement of the first piston element,and the other allowing the flow of fluid in the opposite direction tothe variable volume chamber. Non-return valves may be used to define thedirection of flow in each case. Separate electrical actuators may beprovided for each damping control valve to allow dynamic variation ofresistance to flexion in each direction. Alternatively, one or both maybe manually presettable. It is particularly preferred that the valvecontrol system is adapted such that the actuator drive signal fed to theoutput control valve actuator for dorsi-flexion damping control causesthe damping control valve to increase the orifice area as the indicatedwalking speed increases, thereby decreasing dorsi-flexion dampingresistance with increasing walking speed and vice-versa.

The invention also includes a prosthetic ankle and foot combinationcomprising a foot component and an ankle joint mechanism, whichmechanism includes a proximal mounting interface, the joint mechanismbeing arranged to allow limited damped pivoting of the foot componentrelative to the mounting interface about a medial-lateral joint flexionaxis during use, wherein: the mechanism comprises a hydraulic piston andcylinder assembly and an associated linkage arranged to convert betweentranslational piston movement and rotational relative movement of theproximal mounting interface and the foot component; the piston andcylinder assembly comprises first and second piston elements which aresubstantially coaxial and substantially aligned with the shin axis; thefirst piston element has a neutral position in the assembly and islocated in a cylinder so as to drive hydraulic fluid through an orificewhen moved from the neutral position in response to pivoting of the footcomponent from a preset reference angular position relative to theproximal mounting interface, the fluid flow through the orifice dampingthe said pivoting; and the second piston element is arranged to drive byhydraulic fluid through a locking valve in response to pivoting of thefoot component relative to the proximal mounting interface, which valvecan be closed to lock the second piston element thereby to set the saidreference angular position corresponding to the neutral position of thefirst piston element. As an alternative to setting the reference angularposition via a hydraulic device, other mechanical adjustment devices maybe used to adjust the position of the ankle interface (pyramid device orshin clamp) to accommodate changes to heel height.

According to yet a further aspect of the invention, a prosthetic anklejoint assembly comprises a proximal mounting interface, a distalmounting interface, and a joint mechanism interconnecting the proximaland distal mounting interfaces and constructed to allow dampedrotational movement of the proximal mounting interface relative to thedistal mounting interface about a medial-lateral joint flexion axisduring use, wherein the joint mechanism is arranged to provide acontinuous hydraulically damped range of ankle motion during walkingwith dynamically variable damping resistances associated with anklemotion in the plantar-flexion and dorsi-flexion directions respectively;the ankle joint assembly further comprises a control system coupled tothe joint mechanism having at least one sensor for generating signalsindicative of a kinetic and/or kinematic parameter of locomotion; andthe joint mechanism and the control system are arranged such that thedamping resistances effective over the said range of motion andassociated with motion in the plantar-flexion and dorsi-flexiondirections are adapted automatically in response to the said signals.

The invention also includes a lower limb prosthesis including aprosthetic ankle and foot combination as defined above.

Independent control of plantar-flexion damping resistance assists kneestability in above-knee amputee locomotion by managing the groundreaction vector orientation with respect to the knee joint centrespecifically to diminish the flexion moment about the knee. Thisfunction is useful when for example walking down a ramp; a lower levelof resistance to plantar-flexion allows the foot to realign to thewalking surface without generating substantial reaction moments whichwould otherwise cause the knee to become unstable.

According to yet a further variant, a lower limb prosthesis comprises ashin component, a foot component, a joint mechanism interconnecting thefoot and shin components and arranged to allow limited damped pivotingof the foot component relative to the shin component about amedial-lateral flexion axis during locomotion, and a control systemhaving at least one sensor for generating signals indicative of at leastone characteristic of locomotion, the joint mechanism including a devicefor adjusting, the limit of dorsi-flexion of the foot component relativeto the shin component during locomotion. Typically the control system isarranged to generate signals indicative of walking on stairs or on anincline and to alter the dorsi-flexion limit to increase the maximumdegree of dorsi-flexion permitted by the joint mechanism when suchsignals are produced compared with the degree of dorsi-flexion permittedby the adjusting device when signals are generated indicative of walkingon level ground. A further adjusting device may be included foradjusting the degree of damping resistance of the joint mechanism in thedirections of dorsi-flexion and plantar-flexion respectively in responseto signals from the control system, the control system and the jointmechanism being arranged such that the dorsi-flexion limit and thedamping resistances are independently adjustable during locomotion.

Again, it should be noted that features set out above in relation to alower limb prosthesis may also, according to the invention, be providedin a prosthetic ankle-foot combination or in a prosthetic ankle jointhaving proximal and distal mounting interfaces for shin and footcomponents respectively.

The invention will be described below by way of example with referenceto the drawings.

In the drawings:

FIG. 1 is a sectional view of a lower limb prosthesis incorporating afirst ankle and foot combination in accordance with the invention;

FIG. 2 is a block diagram of a control system forming part of theprosthesis of FIG. 1, shown connected to a pair of servo valves forcontrolling damping resistance;

FIG. 3 is a flow diagram for dynamic damping control;

FIG. 4 is a flow diagram for heel-height adjustment;

FIG. 5 is a sectional view of a lower limb prosthesis incorporating asecond ankle and foot combination in accordance with the invention;

FIG. 6 is a sectional view of a third ankle and foot combination inaccordance with the invention;

FIG. 7 is a sectional view of a fourth ankle and foot combination inaccordance with the invention;

FIG. 8 is a cross-section of an ankle joint mechanism similar to thatshown in FIG. 7, sectioned on an AP plane;

FIG. 9 is an anterior elevation of the ankle joint mechanism of FIG. 8;

FIG. 10 is a diagram illustrating the ankle yielding range afforded by aprosthesis in accordance with the invention; and

FIG. 11 is a diagram illustrating operation of a prosthesis inaccordance with the invention during walking;

FIGS. 12A and 12B are graphs illustrating the dynamic control of dampingresistance during an individual gait cycle;

FIGS. 13A to 13D are graphs illustrating the variation of dampingresistances according to walking surface inclination and walking speed;and

FIGS. 14A and 14B are flow diagrams for dynamic damping control inresponse to walking surface inclination and a combination of walkingrequirements respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring to FIG. 1, a lower limb prosthesis in accordance with theinvention has a foot component 10 with a foot keel 12 comprising a rigidcarrier 12A. Independently coupled to the rigid carrier 12A are a toespring 12B and a heel spring 12C. The keel 12 is largely formed fromcarbon fibre composite material and can be surrounded by a foam cosmeticcovering (not shown).

Coupled to the foot keel 12 is a shin component 14 having, at its distalend, an ankle joint mechanism 16 which is housed largely within the shincomponent 14 and connects the shin component 14 to the foot keel 12. Theshin component 14 defines a shin axis 18. The mounting of the shincomponent 14 to the foot keel 12 is by way of an ankle flexion pivot 20defining a flexion axis 20A running in a medial-lateral direction to theanterior of the shin axis 18. The ankle joint mechanism is in the formof a piston and cylinder assembly, the cylinder 22 of which forms anextension of a shin tube centred on the shin axis 18. The cylinder 22slidably houses two coaxial piston elements 24, 26, the axes of which,in this case, coincide with the shin axis 18. These two piston elementscomprise a first piston element 24 for providing a dynamic dampingaction during locomotion, and a second piston element 26 for independentadjustment of heel-height. As will be understood from the descriptionwhich follows, these two piston elements are able to movetranslationally in the cylinder 22 independently of each other so that aheel-height setting can be established without affecting the function ofdynamic damping action provided by the first piston element.

To describe the piston and cylinder assembly in more detail, the dynamicpiston element 24 has two pistons 24P, 24D interconnected by an axialpiston rod 24R. Located in the space between the two pistons 24P, 24D,the second piston element 26, for heel-height adjustment, is alsoreciprocable within the cylinder in the space between the pistons 24P,24D of the first piston element and, itself, has two spaced, apartpistons, 26P, 26D which are interconnected by a respective piston rod26R. The heel-height adjustment piston 26 has an axial bore running itsentire axial length to house the piston rod 24R of the dynamic dampingpiston element 24. Between the pistons 26P, 26D of the heel-heightadjustment piston element 26 is a transversely extending dividing wall22T which is fixed to the inside of, or is integral with, the cylinder22, thereby dividing the space between the two pistons of the secondpiston element 26 into two annular variable-volume chambers 30A, 30B.

The axial extent of the second piston element 26 is such that a furthertwo annular variable-volume chambers 32A, 32B are created between,respectively, the two proximal pistons 24P, 26P of the piston elements24, 26 and between the two distal pistons 24D, 26D of the two pistonelements 24, 26.

Both pairs of annular variable-volume chambers 30A, 30B; 32A, 32B arefilled with hydraulic fluid.

Running through the body of the dynamic damping piston 24 so as tointerconnect the two annular chambers formed between this piston elementand the heel-height adjusting piston element 26 are two passages 34arranged in parallel, each with a damping control valve 36. (Only onepassage and one such control valve is shown in FIG. 1.) Valves 36 areeach in the form of a tapered valve element threaded in the body of thedynamic damping piston element 24 and driven by a respective electricalactuator in the form of a servo motor 38 to allow variation in the areaof the orifice created by the penetration of the valve element of thevalve 36 into the passage 34. (Again, only one servo motor 38 appears inFIG. 1.) It will be appreciated that operation of the servo motors 38varies the resistance to fluid flow between the outer annular chambers32A, 32B and hence the resistance to movement of the first pistonelement 34 with respect to the second piston element 26. Non-returnvalves 39 (one of which is shown in FIG. 1) located in the passage 34confine fluid flow in the respective passages to flow in response todorsi-flexion and plantar-flexion of the ankle joint so that the orificearea of one valve 36 governs the damping resistance in the direction ofdorsi-flexion and that of the other valve 36 governs resistance in thedirection of the plantar-flexion.

A third valve, for heel-height adjustment and in the form of a lockingvalve 40, is housed in the transverse wall 22T to interconnect the twoinner annular chambers 30A, 30B. This valve is operated by a thirdelectrical actuator 42 and can be opened or closed to allow movement orprevent movement of the second piston element 26 in the cylinder 22respectively.

The translational movement of the piston elements 24, 26 is associatedwith pivotal movement of the foot component 10 relative to the shincomponent 14 about the shin connection axis 20A. This occurs by virtueof the axis 20A being offset from the shin axis 18, and a pivotalconnection and a connecting link 42, 44 between interconnecting thedynamic damping piston element 24 at its distal end and the foot keel12, the link having pivotal connections to each of these two components.Since the pivotal connection axis 20A and the axis of the lower pivotalconnection 48 of the link 44 are spaced apart laterally with respect tothe axis of the piston elements 24, 26, rotational forces acting uponthe prosthetic foot 10 are translated to linear axial forces on thepiston elements 24, 26.

In this embodiment of the invention, there are springs 50A, 50B in theouter annular chambers 32A, 32B biasing the dynamic damping pistonelement 24 to a neutral position with respect to the heel-heightadjustment piston element 26. The springs 50A, 50B are optional. Theneutral position is not defined by the springs 50A, 50B but, rather, isa notional datum with respect to the second piston element 26, in thisembodiment, for the purpose of adjusting the position of the heel-heightadjustment piston element 26.

Control of the electrical actuators 38, 42 is performed by a valvecontrol system 52 which has a first sensor 52A mounted on the keel 12 ofthe foot component 10 and a second sensor (not shown) within the casingof the main part of the control system 52. The first sensor 52A is adual-axis accelerometer having outputs indicative of acceleration of thefoot component both parallel to and perpendicular to the shin axis 18.The second sensor is a magnetic transducer located to sense thepositions of the piston elements 24, 26 in the cylinder 22. Thefunctions of the valve control system include (a) providing anelectrical interlock between the actuators 38, 42 for the valves 36, 40in order that only the pair of damping valves 36 or the locking valve 40is open to prevent them being simultaneously open and (b) to adjust theorifice area determined by the valve 36 dynamically i.e. in real-timeduring locomotion in response to kinetic or kinematic parameters oflocomotion as sensed by the sensors forming part of the control system52.

The latter function of the control system 52 is indicateddiagrammatically in FIGS. 2 and 3 insofar as signals derived from thesensors 52A, 52B within the valve control system 52 are fed to amicroprocessor control unit 52M which processes the received signals toprovide indications of surface inclination and walking speed,specifically determining an “inclination factor” and a “walking speedfactor”. The microprocessor calculates a required resistance level inthe form of valve positions for the control valves 36 and providescorresponding output signals on first and second outputs 52MA, 52MB ofthe control unit 52M to the actuators 38 for the dynamic damping controlvalves 36 to drive their valve elements to the required positions.

The programming of the microprocessor unit 52M is such that the valvecontrolling resistance to rotation in the direction of dorsi-flexion isdriven towards its open position as the indicated walking speedincreases or when an upwardly inclined surface is indicated, and towardsits closed position when the indicated speed decreases or when adownwardly inclined surface is indicated (i.e. in order that theresistance to flexion of the ankle is decreased at higher walking speedsand when walking up an incline).

In a similar manner, the microprocessor causes the valve that controlsresistance to rotation in the direction of plantar-flexion to movetowards its open position as the indicated walking speed decreases orwhen a downwardly inclined surface is indicated, and to move towards itsclosed position when the indicated speed increases or when an upwardlyinclined surface is indicated (i.e. in order that the resistance toflexion of the ankle is decreased at slower walking speeds and whenwalking down an incline).

Operation of the ankle joint mechanism for the purpose of heel-heightadjustment will now be described in more detail. It will be understoodthat the inner piston element, i.e. the heel-height adjustment pistonelement 26, acts as a movable mechanical reference which can be adjustedto compensate for changes in heel-height. The locking valve 40 isnormally set locked so that the inner piston element 26 is locked withrespect to the cylinder 22. This is the situation during the so-called“dynamic response” mode of the valve control system, the dynamic dampingcontrol valve 36 being operated as described above during this mode. Ina second mode of the valve control system, a “heel-height setting” mode,the dynamic damping control valve 36 is driven to its fully closedposition thereby locking the outer piston element 24, i.e. the dynamicdamping piston element, with respect to the inner piston element 26 sothat the other moves in concert with it. In other words, the spacingbetween the two piston elements 24, 26 is fixed. During the heel-heightsetting mode, the locking valve 40 is driven to its open position,allowing the inner piston element 26 to move in the cylinder 22 inresponse to rotational forces applied to the foot 10. In this way,providing the damping piston element 24 is set to a predeterminedposition with respect to the heel-height adjustment piston element 26beforehand, the foot 10 can be set to a required angle with respect tothe shin component 14, whereupon the valve 40 is closed and normaloperation of the valve control system in the dynamic response mode canbe resumed.

Referring to FIG. 4, therefore, heel-height adjustment includes thefollowing steps executed by software controlling the microprocessor inthe valve control system 52. Firstly, the heel-height adjustment mode isinitiated (step 100), then the damping control valves 36 are driven totheir closed position (step 102), after which the locking valve 40 isdriven to its open position (step 104). At this point, the user isinstructed to adopt a comfortable standing posture whilst wearing therequired shoe (step 106). This causes the heel-height adjustment pistonelement 26 to be driven to a new set position, whereupon the lockingvalve 40 is driven to its closed position (step 108) and the controlsystem 52 reverts to its dynamic response mode (step 110).

In the above way, the required range of motion during locomotion and theresistance to flexion during locomotion are maintained irrespective ofthe heel-height setting. Consistency in the dynamic behaviour of theprosthesis in terms of its behaviour with changing walking activitiessuch as walking up or down inclines, on stairs, and walking at differentspeeds, as well as the behaviour of the system when the user isstanding, is maintained. Adjustment errors are avoided by theinterlocking function referred to above.

Although springs 50A, 50B are shown in FIG. 1, biasing the dampingcontrol piston element 24 to a particular position with respect to themechanical reference provided by the heel-height adjustment pistonelement 26, it is preferred that such springs exert relatively smallforces or, indeed, are omitted altogether so that the ankle jointmechanism provides a substantially inelastic yield over its dynamicrange of flexion.

It will be noted that by separating the functions of heel-heightadjustment and dynamic damping control, it is possible to maintain thedamping control valves 36 in a set position so long as the walkingcharacteristics indicated by the sensors 52A, 52B of the valve controlsystem 52 do not change. This means, for instance, that while the useris walking at a constant speed and on a constant gradient, no batterypower is required to alter the valves 36. Power is only consumed by theactuators for the valves 36 when the walking speed or gradient changes.

Referring, now, to FIG. 5, a second lower limb prosthesis in accordancewith the invention has stacked proximal and distal cylinder units 22P,22D. Each piston element 26, 24 in this example has a single piston on arespective piston rod 26R, 24R, each piston being independently movablewithin its own fluid-filled cavity in the respective cylinder unit 22P,22D. Each piston divides its cavity into two variable-volume chamberswhich are interconnected with a respective passage 54, 34, each passagecontaining a respective valve 40, 36. In this case only one dynamicdamping control valve 36 is present. At least one of the valves has anelectrical actuator 38 housed on the wall of the respective cylinderunit 22D.

The distal cylinder unit 22D has anterior extension 22DE housing a pivotaxial 20 for pivotally connecting the cylinder unit 22D to theprosthetic foot keel 12, the pivotal connection defining amedial-lateral connection axis 20A. As in the embodiment described abovewith reference to FIG. 1, a link member 44 pivotally interconnects thepiston rod of one of the piston elements 24 to the foot keel at alocation spaced from the pivotal connection axis 20A so that movement ofthe respective piston element 24 in its cylinder unit 22D is associatedwith rotational movement of the foot component 10 with respect to theshin about the pivotal connection axis 20A.

In this embodiment, a similar pivotal connection exists between the shincomponent 14, of which the proximal cylinder unit 22P is an extension,and the distal cylinder unit 22D. Again, the respective cylinder unit22P has an anterior extension 22PE housing a pivot axle 56 to define asecond pivotal connection axis 56A. Posteriorly spaced with respect tothe second pivotal connection axis 56A is a pivotal connection 58between the piston rod 26R of the piston 26 housed in the proximalcylinder unit 22P so that motion of the piston element 26 in thecylinder unit 22P is associated with pivotal movement between theproximal and distal cylinder units 22P, 22D.

In the illustrated prosthesis, the distal cylinder unit 22D and itsassociated piston element 24 perform flexion damping, the orifice areaassociated with the interconnecting passage 34 being controlledproportionally as in the first-described embodiment, using a needlevalve 36 and servo motor 38. The other cylinder unit 22P and its pistonelement 26, together with associated locking valve 40, performheel-height adjustment, the locking valve 40 being closed during normaloperation, i.e. during the dynamic response mode.

As in the first-described embodiment, the damping control valve 36 isdriven to its closed position during a heel-height adjustment mode ofthe valve control system.

Functioning of the ankle joint mechanism is largely the same asdescribed above in connection with the embodiment of FIG. 1, withreference to FIGS. 2 to 4, the main differences being that only theresistance to dorsi-flexion is dynamically variable and that the pivotaxis 20A is a dynamic flexion axis only rather than an axis serving forboth dynamic flexion and heel-height adjustment. Instead, in this secondembodiment, there is a separate heel-height adjustment axis 56A. Oneparticular feature that this embodiment has in common with the firstembodiment is that movement of the two pistons is cumulative in terms ofthe associated pivoting movement of the foot component with respect tothe shin component 14.

Another feature which the two embodiments have in common is that theaxes of the two piston elements 24, 26 are at least approximatelycoincident, both with each other and with the shin axis 18. Minordeviations from this rule occur in the case of the embodiment describedabove with reference to FIG. 5 insofar as some limiting pivoting occursbetween the axis of the proximal and distal cylinder units 22P, 22Daccording to the set heel-height. The longitudinal orientation of thepiston axes and, with both running at least approximately along the shinaxis, results in a particularly compact arrangement, allowing sufficientspace around the ankle joint mechanism for an ankle cosmesis thatmaintains a required shape.

Although each embodiment of the invention described above is a lowerlimb prosthesis including a shin component 14, an ankle joint mechanism16 and a foot component 10, it will be understood that the inventionalso includes detachable units such as a prosthetic ankle and footcombination or a prosthetic ankle joint, the first having a shincomponent attachment interface on the ankle joint mechanism, and thelatter having both a shin component attachment interface and a footcomponent interface attachment on the ankle joint mechanism. Thismodular approach allows the interconnection of different shin and/orfoot components with the ankle joint mechanism.

Summarizing, it will be seen that, in each of the above-describedprostheses, at least one piston is being used to alter alignment whenthe prosthesis is not being used for locomotion activities, thealignment preferably being controlled electronically to reduce the riskof incorrect adjustment. A second piston, preferably undermicroprocessor control, is used to adapt damping characteristics of theprosthesis by way of a variable yielding action in real-time accordingto changing walking conditions, in particular walking speed and surfaceinclination. Although electronically controlled valves have beendisclosed above, the valves may be manually manipulated or adjusted.Linked valve control means ensure, preferably, that the dynamic controlvalve is closed and not allowed to open when the heel-height adjustmentvalve is open.

Dynamic valve control may be used in both single and double pistonembodiments of the invention. Referring to FIG. 6, a third prosthesis inaccordance with the invention is in the form of a prosthetic ankle joint116 having proximal and distal mounting interfaces 116P, 116D, theformer being in the form of a shin tube clamp defining a shin axis 18and the latter being in the form of a conventional pyramid socket. Thepyramid socket 116D receives a pyramid component 12P attached to a keelpart 12 of a prosthetic foot 10. The shin tube clamp 116P forms part ofa cylindrical housing 114. The housing 114 is mounted to the pyramidsocket 116D by way of an ankle flexion pivot 20 defining a flexion axis20A running in a medial-lateral direction to the anterior to the shinaxis 18, as in the embodiments described above with reference to FIGS. 1and 5. Within the cylindrical housing 114 is a single piston element 124for providing a dynamic damping action during locomotion, the housing114 having a transverse wall 122T separating the space between thepistons 24P, 24D of the piston element 24 into two fluid-filled chambers30A, 30B. Transverse wall 122T includes a valve 136 with an associatedelectrical actuator 138, the valve and actuator acting together to varythe resistance to fluid flow between the chambers 30A, 30B as the piston24 is moved translationally in the housing 114 in response to flexion ofthe foot 10 about the pivot axis 20A, such pivoting movement beingconverted to translational movement of the piston by the link 44 and thepivot 20.

Associated with a proximal extension 24E of the piston 24 is apiston-stroke range control collar 160. The axial position of thiscollar 160 is adjustable in response to operation of a linearelectro-mechanical actuator 162 fixed to the housing 114. The collar 160is shaped to provide at least a dorsi-flexion end-stop for the piston24, thereby limiting the dorsi-flexion of the foot component 10 relativeto the housing 114.

As in the previously described embodiments, an electronic control system52 is mounted to the housing 114. This contains not only a sensor forsensing the position of the piston 24, but also, e.g., a gyroscopesensor for sensing the angular velocity of the housing 114 (and hencethat of a shin tube in the shin tube connector 116P), as well as,optionally, an accelerometer or an inclinometer for measuringacceleration and angular position respectively. As before, the controlsystem 52 includes a microprocessor for evaluating the signals from thesensors to generate signals indicative of not only speed of locomotionand surface inclination, but also terrain variation in the form ofstairs, and whether the amputee is climbing or descending such stairs.The period and magnitude of signal quantities between gait events andtheir occurring sequences can be used for identification of speed andactivity or terrain. Known motion tracking techniques, including thosepublished in the Morris and Hayes et al papers referred to hereinabove,may also be used to determine the gradient of a walking incline andstep-height differentials indicating stair walking.

The microprocessor system forming part of the control system 52processes the signals from the sensors to adjust the two dynamic controlvalves 136 and the piston-stroke range control collar 160 by drivingactuators 138, 162 during locomotion thereby to dynamically adjustdorsi-flexion and plantar-flexion damping resistances and flexion range,in particular to dynamically adjust the dorsi-flexion end stop. It willbe noted that independent control of damping resistances and end-stop ispossible.

Adjustments are performed by the control system 52 actively to adjusthydraulic stiffness and range of motion to optimise locomotioncontinuously when walking at various speeds and on ramps and stairs. Thepiston-stroke range control effectively controls the timing and quantityof energy absorption and storage in the gait cycle, whilst the valves136 determine the rate of energy dissipation. The linear actuator 162may be used to restrict piston travel in a manner independently from thedamping valves 136 with the advantage that the actuated range controlcollar 160 need not be moved on every step, thereby considerablyreducing the time that the control actuators are powered.

Dorsi-flexion damping resistance may be controlled separately fromplantar-flexion damping resistance. Dorsi-flexion resistance isdecreased with higher speeds of locomotion. In this embodiment,plantar-flexion resistance is increased with speed of locomotion. Withregard to the adjustable dorsi-flexion end-stop provided by the rangecontrol collar 160 and its associated actuator 162, the control system52 is arranged to adjust the range control collar 160 downwardly (i.e.in the distal direction) when signals are produced in the control systemindicating, e.g. descent of stairs. Further adjustments of the range offlexion are preferably performed in response to other indications ofchanging terrain.

The provision of a variable end-stop may be achieved in other ways. Forinstance, the dynamic piston control valve 136 can be completely closedduring locomotion under control of the microprocessor in the controlsystem 52 at different angles and times in the gait cycle. This may berequired on every step, depending on selected heel height and thewalking requirements.

As a further alternative, a double piston arrangement as described abovewith reference to FIG. 1 may be used to provide range controlindependently from damping resistance control, the inner piston beingused to alter the piston-stroke range (flexion end-stops).

This may be accomplished by moving the inner piston 26 (see FIG. 1)incrementally and precisely by means of an electrically actuatedhydraulic pump (not shown), the sensor system being used to monitor theposition of the piston 26 by way of a feedback loop. In this instance,the locking control valve 40 (FIG. 1) is replaced by a pump arrangement,thereby providing the means to displace hydraulic fluid between thechambers 30A, 30B so as actively to move the reference piston 26.Alternatively, the reference piston 26 may be moved in known incrementsfrom a predetermined datum position.

In yet a further embodiment, using the arrangement shown in FIG. 1, thelocking valve 40 for locking the reference piston 26 may be used tofacilitate incremental movement of the reference piston 26 duringplantar-flexion and dorsi-flexion phases of locomotion. The forcesproduced during locomotion are used, in this case, physically to movethe reference piston 26, valve 36 (FIG. 1) being closed at appropriatetimes. The control system 52 coordinates valve actuation and monitorsthe reference piston position.

Referring to FIG. 7, another single piston embodiment of the inventionhas a shin component in the form of a pyramid-shaped shin connectioninterface 170 which defines a shin connection axis 172. As in theembodiment described above with reference to FIG. 1, an ankle jointmechanism 18 connects the shin component to the foot keel 12A of thefoot 10, the mounting to the foot keel 12A being by way of an ankleflexion pivot 20 defining a flexion axis 20A.

The body of the joint mechanism 16 forms the cylinder of a piston andcylinder assembly having a piston 24 with upper and lower piston rods24A, 24B, the lower piston rod being pivotally connected to the footkeel 12A at a second pivotal connection 48, this second pivotalconnection defining a second medial-lateral axis which is spaced, inthis case, posteriorly from the flexion axis 20A. It will be seen that,as the body of the mechanism 16 pivots about the flexion axis 20A, thepiston 24 moves substantially linearly in the cylinder formed by themechanism body.

The cylinder is divided into upper and lower chambers 32A, 32B. Thesechambers are linked by two bypass passages in the ankle mechanism body16, one of which is visible in FIG. 7, where it is shown by dotted linessince it is behind the sectioning plane of the drawing. The otherpassage does not appear in FIG. 7 since it is located in front of thesectional plane. However, its configuration is almost identical, as willbe described below. These two bypass passages communicate with the upperchamber 32A of the cylinder via a locking valve 176, described in moredetail below, as a common linking passage 178 which opens into the upperchamber 32A.

The two bypass passages, one of which 34 is shown in FIG. 7, eachcontain a damping resistance control valve 36 which has an associatedactuator in the form of a servo motor 38. Operation of the servo motor38 rotates a valve member of the valve 36 to progressively increase ordecrease the orifice area of the valve 36. The bypass passage 34 alsocontains a non-return valve 39. This adjustable-area orifice valve 36and the non-return valve 39 are arranged in series in the bypass passage34, between the locking valve 176 and the lower chamber 32B.

The bypass passage 34 appearing in FIG. 7 has its non-return valve 39oriented to allow the flow of hydraulic fluid from the lower chamber 32Bto the upper chamber 32A. The other bypass passage (not shown) has itsnon-return valve oriented in the opposite direction. Accordingly, one ofthe passages 34 is operative during dorsi-flexion and the other duringplantar-flexion. When the locking valve 32 is open, continuous yieldingmovement of the foot component 10 relative to the ankle joint mechanism16 about the flexion axis 20A is possible between dorsi-flexion andplantar-flexion limits defined by the abutment of the piston with,respectively, the lower wall and the upper wall of the cylindercontaining the piston. The level of damping for dorsi-flexion andplantar-flexion is independently and automatically presettable by therespective adjustable-area orifices by means of a control system (notshown in FIG. 7) like that described above. The control system, as inthe embodiments described above with reference to FIGS. 1 and 5, has asensor 52A in the form of an accelerometer mounted on the foot keel 12A.

The shin connection interface 170 is conventional, being of pyramidconstruction. Typically, a shin tube is mounted to the shin connectioninterface 170, the shin component having, at its distal end, an annularfemale pyramid receptacle having alignment screws, as well known tothose skilled in the art, for adjusting the orientation of the shin tuberelative to the ankle joint mechanism 16. At a neutral alignmentposition, the axis of the shin tube (the shin axis) is coincident withthe shin connection axis 172 (shown in FIG. 7). When the shin tube isaffixed to the ankle unit 16 in this neutral position, the limit ofdorsi-flexion of the ankle-foot prosthesis, defined by the abutment ofthe piston 24 with the lower wall of the lower cylinder chamber 32B,corresponds to an anterior tilt of the shin axis relative to thevertical when the user stands on a horizontal surface. The plantarflexion limit, defined by abutment of the piston 24 with the upper wallof the upper cylinder chamber 32A corresponds to a posterior tilt of theshin axis.

In this embodiment, the anterior and posterior tilt angles of the shinconnection axis 22 at the dorsi-flexion and plantar-flexion limits are 4degrees (anterior) and 8 degrees (posterior) respectively with respectto the vertical.

In this embodiment, the mechanical end-stops represented by the abutmentof the piston with the lower and upper cylinder walls define a yieldrange over which the ankle-foot prosthesis is free to flex duringlocomotion and during standing, providing the locking valve 176 is open.In this respect, the lower and upper cylinder walls define a yield rangein the same way as the collar 160 of the mechanism described above withreference to FIG. 6. Heel-height adjustment may be performed by alteringthe shin tube alignment. Alteration of the shin component alignment atthe shin connection interface 170 does not alter the angular magnitudeof the yielding range because it is governed by the piston stroke, butit does alter the position of the flexion range limits with respect tothe vertical.

It will be understood, therefore, that the angular range magnitude isfixed by the construction and geometry of the ankle-foot prosthesis andits hydraulic joint mechanism. The degrees of dorsi-flexion andplantar-flexion respectively are altered by the alignment of the shincomponent connection, as described above. It will be understood thatalternative alignment interfaces can be used to adjust the positions ofthe dorsi-flexion and plantar-flexion limits. For instance, ananterior-posterior tilt alignment interface may be provided between theankle unit 16 and the foot keel 12. Such an interface is provided by afurther embodiment of the invention, as will now be described withreference to FIGS. 8 and 9.

Referring to FIG. 8, this further embodiment of the invention takes theform of a two-part ankle joint-mechanism having an ankle unit body 16Awhich, as before, mounts a shin connection interface 170 for adjustableconnection to a shin tube (not shown), and a foot mounting component 16Bwhich incorporates a foot connection interface for receiving a pyramidconnector of the known kind on a foot keel (not shown in FIG. 8). Thejoint mechanism is identical to that described above with reference toFIG. 7 with the exception that the flexion and piston rod connectionpivots 20, 48 are housed in the foot mounting component 16B rather thandirectly in the keel of a prosthetic foot. In the case of FIG. 8, thedrawing is a cross-section on a vertical anterior-posterior planeparallel to but spaced from the axis of the shin connection interface170 and the cylinder housing the piston 24. Consequently, the bypasspassage permitting hydraulic fluid flow from the lower chamber 32B tothe upper chamber 32A of the cylinder (corresponding to dorsi-flexion,i.e. clockwise rotation of the foot mounting component 16B relative tothe ankle unit body 16A about the pivot 20) appears in full lines,whereas the common linking passage 178 between the control valve 176 andthe upper chamber 32A is shown with dotted lines.

It will be understood that the non-return valve 39 has a counterpartnon-return valve in the bypass passage (not shown) allowing for plantarflexion, but that the orientation of that counterpart valve is reversedfrom that shown in FIG. 8, as described above with reference to FIG. 7.

For the avoidance of doubt, it should be pointed out that the bores inthe ankle unit body 16A which house the upper and lower piston rods 24A,24B provide sufficient clearance around the piston rods to allow alimited degree of rocking of the piston 24 and piston rods 24A, 24Brelative to the cylinder as the foot mounting component 16B rotates withrespect to the ankle unit body 16A. The periphery of the piston 24 isshaped so as to have an arcuate cross-section, also for this reason. Thesame features are present in the ankle unit of FIG. 7.

The distal part of the ankle unit body 16A is in the form of a trunnion16AA housing pivot axles of the flexion pivot 20 and the piston rodconnection pivot 48. The foot mounting component 16B has an integralannular female pyramid alignment coupling 16BA. This annular pyramidconnector includes four screws 180, three of which are shown in FIG. 8.

The ankle unit trunnion 16AA is shown more clearly in FIG. 9. Alsovisible in FIG. 9 are two valve adjustment spindles 36A, 36B which areaccessible on the anterior face of the ankle unit body 16A. These formpart of the dynamic damping control valves 36 (or flow resistanceadjusters), one of which appears as valve 36 in FIG. 8, and permitcontinuous electronic adjustment of damping resistance to ankle flexionin the dorsi- and plantar-flexion directions respectively. The servomotors 38 are shown by dotted lines in FIG. 9 in order that thepositions of the valve spindles 36A, 36B can be more clearly seen.

Referring again to FIG. 8, the locking valve 176 is a spool valve havinga spool member 182 which is slidable in a spool valve bore. The bore hasthree ports (not shown). A first port is that of the common linkingpassage 178 communicating with the upper chamber 32A of the cylinder.Second and third ports, offset medially and laterally with respect tothe common passage 178, provide for communication with the bypasspassages 34.

At one end of the spool member 182, there is a manually operablepushbutton 184 (see FIG. 9), which, when pushed against the outwardbiasing force of a stack of spring washers encircling the spool member,moves the spool member 182 to an open position, as shown in FIG. 4.

When the spool member 182 is in its open position, it allows fluid flowbetween the bypass passages 34 and the common passage 178 communicatingwith the upper chamber 32A of the cylinder. Conversely, when the pushbutton 184 is released, the spool member 182 moves to prevent fluid flowbetween the upper cylinder chamber 32A and the bypass passages 36. Itfollows that when the pushbutton 184 is released, the ankle unit ishydraulically locked at whichever flexion angle existed at the moment ofrelease. The pushbutton 184 has a detent that allows it to be maintainedin its depressed position. This is the normal position of the lockingvalve 176, in which flow of hydraulic fluid through the bypass passages36 (FIG. 8) is allowed, with the result that the ankle unit allowsyielding dorsi- and plantar-flexion.

The same locking valve arrangement is present in the ankle jointmechanism of the foot-ankle prosthesis described above with reference toFIG. 7.

Whether the ankle unit is in the form of a two-part assembly fordetachable mounting to a foot component, as described above withreference to FIGS. 8 and 9, or in the form of an ankle joint mechanismdirectly pivotally mounted to a prosthetic foot, as described above withreference to FIG. 7, the joint mechanism allows yielding ankle flexionas shown diagrammatically in FIG. 10. The dotted lines denoteplantar-flexion (PF) and dorsi-flexion (DF) limits of a mechanicalhydraulic yielding range of flexion of a shin component 56 with respectto a foot component 10. The magnitude of the angular range is fixed bythe geometry of the joint mechanism and its damping piston and cylinderassembly. Although in these preferred embodiments, the range magnitudeis fixed, the position of the limits with respect to a neutral positionindicated by the chain lines in FIG. 10 can be altered by adjusting thealignment of the shin component relative to the foot component using oneof the alignable connection interfaces described above. In this way, theflexion range may be biased anteriorly or posteriorly from the positionshown in FIG. 10 to create a larger range of motion in either the PF orDF direction. Typical alignment settings result in a dorsi-flexion limitat 2 degrees to 6 degrees tilt anteriorly with respect to the neutralaxis, dependent on the foot toe spring stiffness in particular, and theplantar flexion limit at 4 degrees to 10 degrees tilt posteriorly withrespect to the neutral axis (shown by the chain lines in FIG. 10).

Providing the manual hydraulic lock is not activated, the unitcontinuously allows yield in the dorsi-flexion direction (andplantar-flexion direction) up to the dorsi-flexion limit during walkingand standing.

The applicants have found that providing a yielding ankle with minimal,preferably zero elastic biasing in the dorsi- or plantar directions, andwith flexion limits set within the above ranges, provides advantagesduring stair walking and ramp walking activities, and during standing.In the normal body, the biomechanics of standing balance control arecharacterised by the natural balancing of external moments between jointcentres of rotation. The geometrical position of the joint centres ofrotations and the relative position of the body centre of gravity andthe reaction vector are important for stabilising action. Limb stabilitywith a prosthetic limb is primarily dependent on geometry, notmuscle-induced internal moments. Consequently, standing can be achievedfor long periods with minimal muscular effort. A small amount ofcyclical postural sway of the upper body also helps to create stability.It follows that natural standing posture and balance control can beachieved with joints exhibiting low levels of internal resistive torque,the position of the ground reaction vector relative to the hip, knee andankle joints being the main source of limb stability. Allowing yield ina prosthetic ankle in the manner provided by the ankle-foot combinationdescribed above aids this function for a lower limb amputee.

The dynamic action of a lower limb prosthesis having the featuresdescribed above during the stance phase of walking is now described withreference to FIG. 11. At heel strike (a), the ankle is in a dorsi-flexedstate from the roll-over actions of the previous step. As the foot movestowards the flat-foot state (b), the ankle plantar-flexes under theaction of the foot heel spring and hydraulic yield at the ankle. Ingeneral, plantar-flexion at the ankle does not reach the plantar-flexionlimit imposed by the joint mechanism of the prosthesis at this stage.During roll-over (c), the ankle begins to dorsi-flex by way of thehydraulic yield afforded by the prosthesis, providing a smooth roll-overaction, preserving body momentum, and improving knee function. Towardsthe end of the roll-over phase (d), the dorsi-flexion limit imposed bythe joint mechanism is reached. Once this happens, mechanical energy isdirected into the keel of the foot (e) to provide energy return forpush-off. The swing phase is initiated with the foot oriented at thedorsi-flexion end-stop to provide toe clearance during the swing phase.

The combination described with reference to the FIGS. 7 to 11 is anfoot-ankle system that is continuously allowed to yield over a limitedrange in plantar-flexion and dorsi-flexion. The yielding action isprovided by a hydraulic damper coupled to conventional foot elements(i.e. keel, carrier and independent carbon fibre composite heel-toesprings). The ankle is, therefore, free to flex continuously over alimited plantar- and dorsi-flexion range via the hydraulic damper withminimal interference from elastic elements during walking and standing.During standing, the relative positions of the hip, knee and ankle jointcentres are such that substantially normal standing postures can bemaintained, the moments about each joint being automatically balancedthereby creating limb stability. Moreover, the self-aligning action ofthe foot-ankle system facilitates improved control of energy transferbetween limb segments during locomotion, the user's hip joint being themain driver and the knee joint being the main facilitator of mechanicalenergy transfer. This biomimetic method of stabilisation of standingstability and balance control has a further advantage in that, whilestanding on ramps, owing to the yielding action of the hydrauliccomponents, there are no significant reaction moments generated aroundthe ankle which may cause imbalance between joints and discomfort.Since, owing to the limited range of hydraulic yielding, the ankle isfree to move, adaptation for walking and standing on inclined surfacesand changes to footwear with various heel heights is achievedautomatically. A further advantage of the system is a smoother moreprogressive transition during roll-over over a variety of terrains.

In all the control embodiments described above, it is preferable thatfunctional parameters such as plantar-flexion and dorsi-flexionresistance levels, profiles (i.e. resistance alteration gradients withrespect to time) and timing, as well as dorsi-flexion range of motionare programmably adjustable. Each of the embodiments may include withinthe control system 52 a receiver for communication with a wirelessprogramming device (not shown). Wireless programming may be performed bya prosthetist during an amputee walking test and tests over differentterrains (e.g. stairs and inclined surfaces) to adjust controlparameters which may or may not be pre-selected by means such as alook-up table to suit the particular amputee's specific locomotion styleand the mechanical properties of attached foot and knee components.Similarly, adaptive control parameters which determine how the abovefunctional parameters are continuously adapted during locomotion anduse, such as walking speed, walking surface gradient, and activitiessuch as stair climbing and descent, are also adjustable underprosthetist control, using control software. Specified and/or measuredadaptive control parameter values may be entered. This may be achievedusing a teaching/playback system. It is also possible to incorporate aself-tuning system whereby control parameters are automatically adjustedtowards specific values under known walking conditions. The changes indamping response may be predefined and contained in a database stored ina storage device forming part of the control system 52, the databasebeing drawn from clinical experience and tests with a plurality ofamputees. Teaching/playback, database, and self-tuning look-up methodsmay be used in combination.

The timing of control of valve function and/or other associateddorsi-flexion limiting means are preferably coordinated duringlocomotion to occur at specific phases of the gait cycle determined fromsystem sensors and using finite state control principles. In this waythe control system can be readily adapted to optimize the mechanicalcharacteristics of the prosthesis, thereby to optimize the biomechanicsof locomotion.

Referring now to FIGS. 12A and 12B, hydraulic flexion damping resistanceand end-stop control may be achieved using a single electricallycontrolled valve. FIG. 12A is a graph plotting the angular velocity ofthe shin component in the sagittal plane during locomotion, obtainedfrom a gyroscope sensor. Control valve and actuator adjustments arecoordinated with respect to detection of gait events such as heel strike(HS) and toe-off (TO), as shown in FIG. 12A using, for instance,zero-crossing trigger points B, C representing the transition betweencounter-clockwise (CCW) and clockwise (CW) angular movement of the shincomponent. In FIG. 12A, the vertical axis represents shin angularvelocity and the horizontal axis represents time, the graph showing acomplete gait cycle. Thus, control valve and actuator adjustments can becoordinated with respect to detected gait events, such as signalzero-crossing events or local signal maxima and minima.

FIG. 12B illustrates damping control valve actuation from a baseresistance level B, a fully closed position D in which the associatedpiston is locked. The shaded region A illustrates an adjustment rangefor commencement of the locked state during the stance phase, resistanceto flexion in the dorsi-flexion direction increasing following heelstrike to a time A which is at a predetermined time interval after atrigger point C represented by the zero-crossing of the shin angularvelocity characteristic prior to heel strike HS. Lock commencement attime A is delayed when the control system 52 detects walking on anincline or stairs (compared to level walking). Thus, flexion isrestricted and/or limited angularly with respect to heel strike. Ineffect, gait-cycle by gait-cycle actuation of the valve as shown in FIG.12B provides variable dorsi-flexion angular limitation. The dotted linein FIG. 12B indicates alteration of the resistance gradient in responseto sensed locomotion characteristics.

The range of motion limit may be specified to occur in response tomeasured characteristics of locomotion such as shin component tiltangle, velocity, or acceleration. Other kinematic or kineticmeasurements made during locomotion may be used.

Over at least the major part of the range of ankle movement, the dampingresistance in the direction of dorsi-flexion remains substantiallyconstant during each step of the locomotion cycle. However, the level ofdamping resistance is allowed to change from step to step according tosignals generated in the control system in response to sensor outputs.The same applies to the damping resistance in the direction ofplantar-flexion. In general, at any point within the range of anklemovement, the damping resistance can be set to any of several differentvalues in response to such control system signals.

Indeed, the level of damping resistance in both dorsi-flexion andplantar-flexion directions is continuously variable over a range ofresistance level values, the limits of the resistance level range beingdetermined by the maximum and minimum orifice areas of the dynamicdamping control valves.

The control system may be programmed to alter damping resistance fromstep to step in a number of different ways. In one configuration thechange in damping resistance in the directions of both dorsi-flexion andplantar-flexion are linearly related to a sensed parameter. Forinstance, as shown in FIG. 13A, the damping control valves can beadjusted linearly between their open and closed positions according tosurface inclination. The damping levels and the valve settings indicatedin FIG. 11A at A represent the dynamic plantar-flexion/dorsi-flexionbalance set for level walking.

Referring to FIG. 13B, the control system may be programmed such thatthe optimum dorsi-flexion and plantar flexion damping levels are unequalfor level walking. Such levels are determined by programming the controlsystem to suit an individual amputee's preferred walkingcharacteristics. As shown in the example of FIG. 13B, the optimum levelof resistance to rotation in the direction of dorsi-flexion is less thanthat in the direction of plantar-flexion. However, according to therequirements of the amputee, the opposite may also be true.

Either or both the resistance in the direction of dorsi-flexion and theresistance in the direction of plantar-flexion may be non-linearlyrelated to the sensed surface inclination. In the example shown in FIG.13C, the response in the direction of plantar-flexion is non-linearlyrelated to surface inclination, while the response in the direction ofdorsi-flexion is linear. Either one or both of plantar-flexion anddorsi-flexion responses may be non-linear or linear according to thevalue of the sensed parameter.

It will be noted that in each of the above examples, the resistance inthe direction of plantar-flexion increases with increasing upwardsurface inclination and decreased with increasing downward surfaceinclination, whereas the resistance in the direction of dorsi-flexionvaries in the opposite sense.

Typical responses in damping resistance to changes in walking speed areshown in FIG. 13D. As will be seen, at a normal walking speed orcadence, the resistance in the direction of dorsi-flexion in thisexample is higher than the resistance to plantar-flexion. As walkingspeed or cadence increases, the resistance in the direction ofplantar-flexion increases whilst that in the direction of dorsi-flexiondecreases. The converse changes apply at slower walking speeds orcadences. In this case, the variation in damping resistances is linear.Non-linear functions may also be programmed in the control system.

In the preferred system, the settings of damping resistance remainconstant over at least the major part of the range of ankle movement,and change from step-to-step according to changes in the sensedparameter using the functions described above with reference to FIGS.13A to 13D. For a given heel-height setting, the range of ankle jointmotion may be fixed, or it may be varied using variable hydraulic ofmechanical end stops, as described above.

The changes in walking requirements may be determined on an individualstep-by-step basis or they may be determined based upon a measuredaverage of a previous number of steps of a specific variable such aswalking speed, cadence, surface inclination or other measured gaitvariable.

The control system may be programmed to divide the range of sensed orcomputed parameter values into bands or sub-ranges, so that changes indamping resistance are triggered only when the relevant parameter valuechanges to the extent that it falls within a different range frompreviously. The overall range of values of the sensed or computedparameter may be divided linearly as shown by the uniform spacing ofsurface inclination or walking speed values in the graphs of FIGS. 13Ato 13D, or non-linearly, for instance according to a square law or alogarithmic function. In other words, the boundaries between bands maybe uniformly or non-uniform. They may also be preset or continuouslyadaptive according to stored gait characteristic histories. Non-linearrelationships between damping resistance and the sensed or computedparameter typically result in increasingly large changes in resistancelevel as the value of the controlled parameter deviates further from acentral value (i.e. from level surface inclination or normal walkingspeed, for instance).

The control system may be programmed to follow different sequences forthe purpose of adjusting valve openings in response to changes in sensedor computed parameters. Referring to FIG. 14A, a first typical sequencefor adapting valve openings to sensed walking surface inclinationinvolves the steps of reading sensor signals indicative of kinetic orkinematic parameter values (step 200), computing the walking surfaceinclination, preferably on a step-by-step basis, the inclination beingcompared to preset inclination bands (step 202), whereupon the systemthen determines whether a change in inclination has occurred (step 204).If no change has occurred, the sequence loops back (loop 206) to repeatthe determination of surface inclination and comparison steps 202, 204,this process continuing until a change is detected. When a change isdetected, required damping resistance levels are computed, e.g. byreference to a look-up table mapping resistance levels to parameterbands (step 208), whereupon actuating signals are fed to the servomotors (or stepper motors) connected to the valves which control dampingresistance to ankle rotation in the direction of plantar-flexion anddorsi-flexion respectively (steps 210A, 210B).

In a more sophisticated control sequence, shown in the flow diagram ofFIG. 14B, similar steps are performed. In this case, the initialdetermination step 302 involves the computation of any of a number ofparameters, including surface inclination, walking speed, cadence,stride length and step height (for climbing or descending stairs). Eachderived parameter is then compared with previously stored values (step304) and, if a change has occurred, net required damping levels arecomputed according to pre-programmed rules in order to move the dampingcontrol valves (steps 310A, 310B).

The prostheses described above incorporate one or both of anaccelerometer mounted on the keel of the foot component and a magneticpositional sensor for piston position sensing. Accelerometers may bemounted in other locations, for instance on a shin tube. Rotary orlinear position sensors may be used. Strain gauge sensors may be used tomeasure ankle forces and moments. Piezoelectric bending sensors may beincorporated for measuring energy storage within foot springs (e.g. toespring 12B (FIG. 1)). Such piezoelectric devices may be used forgenerating electrical energy (e.g. for charging batteries supplyingpower to the control system 52 (FIG. 1)). In this way, electrical energymay be generated on every step.

In the preferred embodiments of the invention, optimum levels of dampingresistance in the directions of plantar-flexion and dorsi-flexion areobtained to provide an adaptive dynamic balance which suits anindividual amputee's gait in different situations and for differentwalking requirements. The nature of the adaptive dynamic balance is thatit has the effect of acting like a brake and an accelerator on themotion of the shin. Optimising these effects for different walkingsituations produces a more stable gait, placing less physiologicaldemand on the amputee to control proximal joints, i.e. the knee and/orthe hip through muscular control, and also with reduced stress at thestump interface.

What is claimed is:
 1. A prosthetic ankle and foot combinationcomprising: a foot component and a hydraulic ankle joint mechanism, theankle joint mechanism including a shin component and being constructedto allow damped rotational movement of the foot component relative tothe shin component about a medial-lateral joint flexion axis, the anklejoint mechanism further including: a piston and cylinder assembly havinga first piston element providing a damping function, the first pistonelement being movable in a cylinder to drive hydraulic fluid through afirst valve defining a first orifice in response to rotation of the footcomponent relative to the shin component, the piston and cylinderassembly further including a second piston element and a locking valve,wherein the second piston element is arranged to drive hydraulic fluidthrough the locking valve in response to rotation of the foot componentrelative to the shin component, wherein the ankle joint mechanism isarranged to provide: (a) continuous hydraulically damped ankle flexionduring walking relative to a preset reference angular position of thefoot component with respect to the shin component when the first valveis open and the locking valve is closed such that the first pistonelement drives the hydraulic fluid through the first orifice, and (b)adjustment of a position of a second piston element with respect to theshin component during use when the first valve is closed and the lockingvalve is open to adjust the reference angular position independently ofthe damping function of the first piston element.
 2. The combinationaccording to claim 1, wherein the mechanism comprises an electricalactuator for driving the first valve to vary the area of the firstorifice thereby to provide dynamically variable hydraulic damping ofankle flexion during walking.
 3. The combination according to claim 2,wherein the mechanism comprises a second valve defining another orificethrough which hydraulic fluid is driven when the first piston elementmoves in response to rotation of the foot component relative to the shincomponent, the first and second valves being constructed and arrangedsuch that the first valve and the second valve independently andrespectively determine a damping resistance of the mechanism to flexionin dorsi-flexion and plantar-flexion directions.
 4. The combinationaccording to claim 2, wherein the ankle joint mechanism is arranged toprovide damped adjustment of the reference angular position, the lockingvalve can be closed to lock the second piston element thereby to set thereference angular position of the foot component with respect to theshin component.
 5. The combination according to claim 1, wherein: theankle joint mechanism comprises a linkage arranged to convert betweentranslational piston movement and rotational relative movement of theshin component and the foot component; the first and second pistonelements are substantially coaxial and substantially aligned with a shinaxis; the first piston element has a neutral position in the assemblyand is arranged to drive hydraulic fluid through the first orifice whenmoved from the neutral position in response to rotation of the footcomponent from the preset reference angular position relative to theshin component, fluid flow through the first orifice damping saidrotation; and the locking valve can be closed to lock the second pistonelement thereby to set said reference angular position corresponding tothe neutral position of the first piston element.
 6. The combinationaccording to claim 5, wherein the first piston element is slidable in abore formed in the second piston element.
 7. The combination accordingto claim 6, wherein the first piston element forms a transverselyextending movable wall of a chamber housing the second piston element.8. The combination according to claim 7, wherein the second pistonelement has two pistons interconnected by a piston rod and is slidablewithin the said cylinder, wherein the two pistons are spaced apart todefine a space between the two pistons, and further comprising adividing wall dividing the space into two variable volume chambers whichare interconnected by a first passage containing the locking valve. 9.The combination according to claim 8, wherein: the cylinder has atransverse wall forming the dividing wall dividing the space between thepistons of the second piston element; and the transverse wall containsthe first passage and locking valve linking the variable volume chambersformed on the opposite sides of the transverse wall.
 10. The combinationaccording to claim 5, wherein the piston and cylinder assembly comprisesfirst and second cylinder units which are pivotally interconnected andwhich house the first and second piston elements respectively, thesecond piston element being pivotally connected to the first cylinderunit such that movement of the second piston element in the secondcylinder unit is associated with pivoting of one cylinder unit withrespect to the other, and wherein the first cylinder unit and the firstpiston element housed therein are respectively pivotally connected tothe shin and foot components such that movement of the first pistonelement is associated with pivoting of the first cylinder unit withrespect to the foot to which it is pivotally connected.
 11. Thecombination according to claim 5, further comprising an interlockingdevice associated with the first valve and the locking valve to preventsimultaneous opening of the locking valve and the first valve.
 12. Thecombination according to claim 1, including a control system arranged togenerate a signal indicative of terrain and to adjust the ankle jointmechanism to vary a hydraulic damping resistance to ankle motion inresponse thereto.
 13. The combination according to claim 12, wherein thecontrol system is arranged to detect walking down a ramp and, inresponse to such detection, to adjust the ankle joint mechanism toreduce the damping resistance to plantar-flexion.
 14. A lower limbprosthesis including an ankle and foot combination according to claim 1.